1. Field of the Invention
The present invention relates to a substrate transportation container and, more specifically, to a hermetic substrate transportation container used for transportation of electronic substrates such as semi-conductor wafers or liquid crystal substrates.
2. Description of the Related Art
Conventionally, an electronic appliance using an electronic substrate, such as a semi-conductor wafer, a liquid crystal substrate or a magnetic disc, is fabricated in a clean room that is free of dust. However, transportation of the electronic substrate between processing apparatuses during fabrication is done by housing an electronic substrate into a cassette inside a portable and sealable clean container (in other words, a substrate transportation container). By means of that, the electronic substrate can be transported without being exposed to dust in the air, both inside and outside of the clean room. Such a substrate transportation container is commercialized under a trade name of SMIF (Standard Mechanical Interface) pod (a trademark of Assist Technologies, Inc.).
Although such SMIF pod has its interior sealed so as to prevent contamination by dust from the air, small molecules such as oxygen, water moisture or volatile organic substances can easily infiltrate. As a consequence, such small molecules infiltrated during transportation between processes contaminate the electronic substrate inside. For example, natural oxide film grows in the surface of the semi-conductor wafer and molecular adsorption contamination by an organic substance, boron, phosphor and the like is originated. For an advanced technology device, such contamination greatly affects the properties of the device.
In view of such problems, a flange is provided in borders of an aperture of the container""s body and by sealing with an O-ring provided in a rim of a base lid to such flange, the sealing properties of the substrate transportation container""s interior are improved. Japanese Patent Laid-Open No. 10-56050 discloses a substrate transportation container that limits infiltration of small molecules. Still, when transporting an electronic substrate that requires high cleanliness, like a semi-conductor wafer, the interior of the substrate transportation container containing the substrate is filled with an inert gas (hereinafter referred to simply as inert gas), such as argon (Ar) or nitrogen gas (N2). At this event, replacement of the interior ambient atmosphere of the container with inert gas is done each time of the open-close of a bottom lid and, as a result, contamination of the electronic substrate by molecular adsorption of organic substances, boron or phosphor as well as formation of natural oxide film on the electronic substrate surface is prevented.
However, a substrate transportation container of the construction mentioned above is constructed using plastics material such as polycarbonate, for example. Because polycarbonate is a high hygroscopic material with a water absorption rate of 0.2%, water moisture is gradually ejected from the internal wall according to time course. As a result, the moisture concentration in the interior of the sealed substrate transportation container cannot be kept low for a long time, thus causing formation of natural oxide film in the surface of the electronic substrate placed inside.
In addition, although the container has to be cleaned up when the interior of the container is contaminated by fine particles, there is a problem that IPA (isopropanol), which is a washing liquid having electron-removing effect, cannot be employed, as IPA is corrosive to polycarbonate.
On the other hand, when constituting a substrate transportation container by means of metallic material with the purpose of controlling moisture discharge from the internal wall, the moisture concentration within the substrate transportation container can be kept low. However, it is hard to consider that a substrate transportation container made of metallic material is suitable for transportation because it is heavily. Furthermore, as the substrate transportation container made of metallic material is formed from a cutting process, productivity is low, and cost is high. Besides, there is the problem that an electronic substrate stored inside cannot be detected from outside, like through infrared radiation.
It is an object of the present invention to provide a substrate transportation container for sealing an electronic substrate by allowing long term conservation of low internal moisture concentration, thus reducing generation of natural oxide film on the electronic substrate surface and permitting recognition of the electronic substrate within the container under the sealed condition.
A substrate transportation container of the present invention achieving such purpose comprises a container body having an aperture for loading and unloading an electronic substrate, the substrate transportation container including a lid for sealing the aperture and at least one member selected from the container body and the lid is constituted mainly by an amorphous polyolefin.
In such substrate transportation container, the container body and the lid have a hygroscopic amorphous polyolefin of low moisture adsorption as a main constituent in its composition. As a result, water discharge from an internal wall of the container is reduced and an increase of moisture concentration within the sealed interior is reduced, even when the container is sealed for a long time. In addition, as the amorphous polyolefin has transparency, an electronic substrate placed inside can be detected, even when the container is sealed.
With such container body and such lid having the hygroscopic amorphous polyolefin of low moisture adsorption as a main constituent in its composition, the moisture discharge from the internal wall of the container is reduced and an increase of moisture concentration within the sealed interior is reduced, thus it is possible to reduce generation of natural oxide over a surface of the electronic substrate stored therein.